Compositions – Preservative agents – Anti-oxidants or chemical change inhibitants
Reexamination Certificate
1998-05-27
2001-08-28
Warden, Jill (Department: 1743)
Compositions
Preservative agents
Anti-oxidants or chemical change inhibitants
C252S405000, C424S405000, C424S409000
Reexamination Certificate
active
06280657
ABSTRACT:
The present invention is directed to biocide solutions particularly suitable for addition to silicone caulks.
BACKGROUND OF THE INVENTION
A variety of products contain biocides to prevent their pre-mature degradation caused by microbial growth and/or to prevent unsightly appearance caused by microbial staining. Important biocides, and biocides of particular interest herein, are phenoxarsines and phenarsazines, 10,10′-oxybisphenoxarsine (OBPA) being of particular interest, and isothiazolinones, 4,5 dichloro-2-n-octyl-4-isothiazol-3-one and 2-n-octyl-4-isothiazol-3-one being of particular interest.
For ease of handling, e.g., to prevent powdered materials from diffusing into the air and creating hazardous conditions at the workplace, many biocides are packaged as concentrates. Liquid concentrates typically comprise a biocide and a solvent for a biocide, and very often contain an additional functional component, such as a plasticizer, when the biocide concentrate is to be incorporated in a plastic composition. Examples of liquid biocide concentrates are found in U.S. Pat. Nos. 4,711,914, 4,761,247, 4,891,391, and 5,498,344, the teaching of each of which are incorporated herein by reference.
Among products to which biocides are commonly added are silicone caulks. The term “caulk” is used herein broadly to include silicone elastomers useful as sealants, adhesives, etc. Most commercial silicone caulks are based on silanol-terminated polydimethyl siloxanes, although the pendant groups may be, to a greater or lesser extent, other than methyl, e.g., phenyl, cyanoethyl or trifluoropropyl. Tri- and tetra-functional silanes serve as cross-linking agents, the functional organic groups of such silanes being, for example, alcohols, carboxylic acids, amines, ketoximines, aldoximes, and amides. Acetic acid, is the most common functional group of cross-linking silanes; dissociation of the acetic acid group from the silane during curing being responsible for the vinegar smell associated with many such caulks. Accordingly, where odor is of concern, silanes with other functional groups, such as ketoximes (e.g., methylethylketoxime) are used. Caulks generally contain fillers, such as silica. In two-part caulks, a condensation catalyst, such as a tin soap, is contained in a part separate from the polysiloxane. One-part caulks are produced in entirely anhydrous conditions and rely on diffusion of moisture from the air to effect a cure. One-part caulks may rely entirely on moisture to effect a cure, but in some cases may contain a condensation catalyst. Both two-part and one-part silicone caulks undergo room temperature vulcanization (RTV).
Currently, a biocide concentrate for silicone caulks comprises OBPA as the biocide, nonylphenol as the solvent, and a silicone oil, particularly poly(dimethyl siloxane). The poly(dimethyl siloxane) acts to compatibilize the biocide with the polysiloxane of the caulking composition to which it is added. Some silicone caulk producers use a composition comprising OBPA, isodecanol and the plasticizer di-(2-ethyl hexyl) phthalate. 2-ethyl-1,3-hexanediol has also been used as an OBPA solvent in silicone caulks. In such compositions, the solvents and any plasticizer are non-volatile and remain in the silicone caulk as it cures. The solvents and di-(2-ethyl hexyl), however, are viewed as adulterants, having uncertain effects on the final product. Nonylphenol yellows some compounds upon exposure to sunlight.
Many biocides, such as OBPA 4,5 dichloro-2-n-octyl-4-isothiazol-3-one and, 2-n-octyl-4-isothiazol-3-one have low solubility in many organic solvents. Furthermore, selection of appropriate solvents is complicated because (1) the solvent cannot interfere with the RTV reaction; (2) the oligomers used in the caulk are somewhat viscous (3) the aesthetic properties of the caulk, such as color and odor are important, and (4) there are many formulators of proprietary caulk formulas with a wide range of formulas to satisfy different physical property requirements such as flexibility, white-pigmented, adhesion to glass, metal, etc. It has proven difficult to find a solvent for anti-microbials that does not detract from one or another desired attribute discussed above. Also, it is not common in the silicone caulk industry to add volatile compounds, with the exception of the functional groups of the silane which volatalize during the room temperature vulcanization.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, there is provided a concentrate of a biocide in a ketoxime having the formula C
1-3
alkyl—C(═N—OH)—C
1-3
alkyl. The biocide is present at at least about 1 wt %, preferably between about 5 and about 10 wt %, up to the limit of solubility of the biocide in the ketoxime; the ketoxime being present in sufficient quantity to dissolve the biocide, up to the balance of the concentrate. The preferred ketoxime is methylethylketoxime (MEKO).
In accordance with another aspect of the invention a concentrate comprises at least about 1 wt %, preferably between about 5 and about 10 wt % of a biocide, between about 30 and about 70% of a functional liquid carrier, plus sufficient ketoxime having the formula C
1-3
—C(═N—OH)—C
1-3
to dissolve the biocide, up to the balance of the composition.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
Herein it is surprisingly found that ketoximes are good solvents for hard-to-dissolve biocides, such as OBPA, 4,5 dichloro-2-n-octyl-4-isothiazol-3-one (DCOIT), 2-n-octyl-4-isothiazol-3-one (OIT), and 5-chloro-2-(2,4-dichlorophenoxy) phenol (TCCP). MEKO as a solvent for DCOIT is especially valuable as this biocide is poorly soluble in propylene glycol, a commonly used solvent for biocide concentrates. TCCP is not soluble in typical silicone oils, but through the use of the ketoxime can be introduced into silicone fluids. From a commercial availability standpoint, MEKO is the currently preferred ketoxime. Also, because MEKO is a known functional group of silane crosslinking agents used in silicone caulks, its compatibility with such systems is known. As such, ketoximes as biocide solvents should be readily acceptable to the industry. Other ketoximes of the above-formula are also suitable.
Isothiazolinones are generally soluble in MEKO. MEKO is most advantageous for dissolving isothiazolinones which are difficult to dissolve in water or other solvents. Additional specific isothiazolinones which may be dissolved in MEKO include, but are not limited to 4,5-dichloro-2-cyclohexyl-3-isothiazolinone (CHXIT), 5-chloro-2-methyl-4-isothiazolin-3-one, and 2-methyl-4-isothiazolin-3-one. Of the phenoxarsines, OBPA is of most commercial interest.
The best economy of materials is achieved with a relatively concentrated biocide product which minimizes the amount of the ketoxime solvent used to formulate the silicone compound. However, for mixing efficiency, it is preferable to introduce low-addition level performance additives, such as biocides, in the presence of bulkier component(s), (represented by the ketoxime and optional cosolvent). This is particularly advantageous when the composition is difficult to mix, which is a property of caulks and the silicone polymers that are used to compound the composition.
Therefore, the preferred composition of the invention will be a balance of (1) high concentration for economy of solvent usage (2) optimal match of mixing equipment and requirements over a range of viscosities, and (3) the optimum use level of biocide to achieve the level of performance in the service-life of the silicone caulk. Much of the literature shows that the biocide use levels are from 0.01 wt % to 0.5 wt % with 0.05-0.1 wt % being most common. A satisfactory mixing ratio for normal equipment is 1 part biocide concentrate to 99 parts silicone caulk components. Taking these factors into consideration, a generally useful concentrate will contain between about 5 and about 10 wt % biocide active ingredient.
The ketoxime must be present at a sufficient amount to dissolve the biocide. The amount of ketoxime necessary
Cross LaToya I
Rohm and Haas Company
Rosedale Jeffrey H.
Warden Jill
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